Technical Abstract:
Climatic, nutritive, and disease-parasite environments of the tropics generally favor the use of cattle with varying percentages contributed by Bos indicus breeds because of their higher level of general adaptability to stressful environments than Bos taurus breeds of cattle. Response cap- ability for beef production characters is generally low in most breeds of Bos indicus cattle. Breeds of Bos taurus cattle have the additive genetic merit to respond for both milk and beef production. Economic and technolo- gical considerations generally do not permit modification of the natural environment of most major ecological zones of the tropics to the degree necessary so that their general adaptability is appropriate to realize a high percentage of the most feasible approach to synchronizing cattle genetic resources with other production resources of the tropics is to achieve some improvements in the natural environment and to use cattle that tpossess the most nearly optimum additive genetic (breed) composition con- tributed by both Bos taurus and Bos indicus breeds through composite breeds. High levels of heterosis can be sustained in rotational cross- breeding because retention of heterosis is proportional to retaining heterozygosity. However, the wide fluctuation in additive genetic (breed) composition between generations in rotational crossbreeding systems may not permit achievement and mainteneance of the most optimum contribution by each breed.